Stressed membrane liquified gas container



22, 1967 J. 5. CLARKE E AL STRESSED MEMBRANE LIQUIFIED GAS CONTAINER 2Sheets-Sheet 1.

Filed June INVENTORS JAMES S. CLARKE CHRISTOPHER E. LOESER ATTORNEY Aug.22, 1967 J. s. CLARKE ET AL 3,337,079

STRESSED MEMBRANE LIQUIFIED GAS CONTAINER Filed June 4, 1965 2Sheets-Sheet 2 INVENTORS JAMES S. CLARKE CHRISTOPHER E. LOESER ATTORNEYUnited States Patent ()fiice 3,337,079 Patented Aug. 22, 1967 3,337,079STRESSED MEMBRANE LlQUIFlED GAS CONTAKNER James S. Clarke, Cranford, andChristopher E. Loeser, Scotch Plains, N.J., assignors to Esso Researchand Engineering Company, a corporation of Delaware Filed June 4, 1965,Ser. No. 461,274 9 Claims. (Cl. 220-15) This invention relates ingeneral to the storage of liquids at cryogenic temperatures and inparticular to improvements in the construction of containers for thestorage of liquified natural gas (LNG). The invention further relates toan improved insulated double walled container for the storage of LNG onboard a tanker vessel.

In the handling of liquified natural gas at atmospheric pressure thesevere low temperature environment introduces numerous criticalstructural and cost considerations into the design of stroage containerstherefor. One of the particularly difficult structural problems centersabout the need for providing for large thermal contractions andexpansions, associated With the reduction of temperature from ambienttemperature down to the service temperature of approximately -259 F.Further difiiculty centers about the choice of materials for thecontainer walls which, of necessity, must be of a type which retaintheir structural properties at this low temperature. Normal carbonsteels embrittle at cryogenic service temperatures and may not beemployed for such use. Other materials such as aluminum, Invar,stainless steel, nickel, etc., while retaining their structuralproperties at the cryogenic service temperature of the stored materialare costly.

Accordingly, it is the principal object of this invention to provide -anovel improved container capable of safely with standing the stressesinduced by the thermal load of the stored material as well as acontainer which employs a minimum of high cost structural members suchas Invar or stainless steel.

In accordance with the invention, a novel double walled container isprovided wherein the inner walls or primary barrier of the container isformed of Invar or other similar property material. The walls of theprimary barrier are formed as membranes and held in a relatively tautflat plane about their peripheries in a framework exterior of the coldtemperature interior of the storage tank. The hydrostatic load of thestored material is supported by a secondary container wall outside ofthe membrane to which the load is transmitted by a layer of insulationmaterial placed between the inner and outer walls.

A feature of the present invention is that it provides a novel means forproducing a flat walled polygonal insulated container for the storage ofcryogenic liquids with a minimum of high cost materials, such as Invar.Another novel feature is that the need for expansion joints in the innerwall of the container is eliminated due to the selection of a materialwith optimum thermal characteristics operating in a non-criticalstressed condition. In accordance with the invention, the outerperiphery of each of the inner walls of the container is provided with aplurality of protruding projections which extend through the plane ofthe adjacent walls. The outer edges of each of the projections aresecured to an outer framework lying in the plane of each of the walls.The outer framework supporting the inner walls of the container absorbsthe contractive thermal load of the inner membrane walls as it cools tothe service temperature. The hydrostatic load of the stored cargo withinthe container is transmitted transversely first through the innermembrane, and then the insulation means to the outer container wall.Because the outer container wall is [fully insulated from the lowtemperature cargo, it may be made of any suitable structural carbonsteel. In this way, a novel low cost insulated container may beconstructed for the storage of liquids at cryogenic temperature.

Accordingly, it is a principal object of the present invention toprovide a novel low cost storage container for liquids at cryogenictemperatures.

A further object of the invention is to provide a novel fiat walledpolygonal container.

A further object of the invention is to provide a novel cryogeniccontainer not requiring expansion and contraction joints.

A further object of the invention is to provide a novel containerwherein the inner wall is of membrane thickness incapable of supportingthe hydrostatic load of the stored liquid and wherein a layer ofinsulation exterior of the inner membrane wall transmits the hydrostaticload to the outer container walls.

These and other objects and advantages of the invention will becomeapparent and the invention will be understood from the followingdescription and drawings in which:

FIGURE 1 is a cross-sectional view of one form of the invention as itwould be located in a typical tanker vessel;

FIGURE 2 is a perspective view, with portions broken away, showing thecorner construction of the invention; and

FIGURE 3 is a cross-sectional view similar to FIGURE 1 showing amodified form of the invention.

Referring to the drawings and FIGURES 1 and 2 in particular, a tankervessel 10 shown schematically in crosssection includes an outer hull 12and winner hull 14 spaced therefrom. An insulated cargo tank 16 inaccordance with the invention is located within the hold of the tankervessel and maintained in spaced relationship therefrom by a plurality ofmain structural members designated 18. In the form shown, the structuralmembers 18 have a generally I-shaped cross-section, one end of whichengages the inner hull 14 while the opposite end serves to secureportions of the outside container plating 26 of the insulated container.As will be explained hereafter, selected structural members 18 alsoserve to support and hold the inner membrane walls of the container in astressed relationship. The cargo tank 16 includes a conventional riserportion designated generally at 20 through which loading and unloadingmay be accomplished.

The novel LNG storage tank in accordance with the invention includes -aplurality of inner membrane panels preferably made of Invar, a materialcapable of withstanding the service temperature and having a lowcoefficient of thermal expansion. Each of the inner membranes 22 definesa substantially fiat plane and includes a plurality of projecting tabportions 28 which extend through a surrounding layer of insulation 24and are secured at their edge portions by welds 30 to the inner surfaceof the main structural frame member 18. As best seen in FIGURE 2, eachof the projecting tabs 28 is rectangular in shape and is ofsubstantially equal lateral width so that they interlock with the tabsof the adjacent intersecting membranes 22 to form an inner line ofintersection on the interior of the cargo tank 16. An interior (orexterior) weld 32 is formed along this common intersection line totightly seal the inner membranes 22 against liquid leakage.

In operation, each of the intersecting frame members 18 forms agenerally rectangular outer boundary for its associated membrane. Eachof the planes defined by the rectangular structure 18 serves to supportthe outer projections of its associated membrane wall 22. Thestructuralrnembers 18 also provide support for the outside plating orsecondary barrier 26 which may be made of any suitable strong materialsuch as carbon steel to withstand the hydrostatic load of the LNG cargo.Upon introduction of the LNG cargo, the lowering of temperature causes acontraction of the membranes 22 which due to the use of Invar isrelatively minor in nature. Therefore, the structural stress limit ofthe inner membrane'ZZ is not exceeded and no plastic deformation thereofwill occur. The insulation blanket 24 is designed to take thehydrostatic load of the cargo and transmit this force to the outerplating 26 which due to the insulation will not assume the low operatingtemperature of the LNG cargo. In this way, novel storage containerarrangement has been provided for a cryogenic liquid employing a minimum amount of relatively expensive material such as Invar or stainlesssteel. The secondary or outer barrier formed by the plating 26 iseffective to take the hydrostatic load of the cargo. The thermalcool-down stresses are taken up by the inner membrane and transmitted tothe main structural members 18 forming a framework about the peripheryof the projections 28.

Referring to FIGURE 3, an alternate form of the invention is disclosedwherein a ships hull 34 includes an inner hull 36 and transversebulkheads 40 of conventional form. The inner hull 36 and bulkhead carrya plurality of membrane supporting members 38 which extend through aninsulation layer 42. The inner end of each of the membrane supports 38is weldably secured at 46 to an inner membrane member 44, preferablymade of Invar. In this embodiment it should be noted that the periodicrigid attachment of membrane 44 by welds 46 to the supports 38, and thechoice of the membrane from a material such as Invar, avoids the needfor provision of expansion and contraction joints. In this way, as inthe embodiment of FIGURES 1 and 2, the inner membrane may be made ofsufficiently thin structure so that it need only support the load due tothe induced thermal stress of initial cooldown of the tank. All thehydrostatic loads are transmitted through the membrane 4-4- andinsulation 42 to the outer carbon steel ships hull 36 and bulkheadmembers 40.

While two specific embodiments of the invention have been described andshown in detail to illustrate the application of the inventiveprinciples, it will be understood that the invention may be embodiedotherwise without departing from such principles. For instance, whilethe invention has been described as having particular utility inassociation with tanker vessels, it will be readily seen that theinvention has equal utility for shore based storage facilities of anypolygonal shape.

What is claimed is:

1. A flat walled polygonal container for storage of liquids at cryogenictemperature comprising a plurality of first wall means defining an innerprimary container, a plurality of second wall means surrounding andspaced from said inner primary container defining an outer secondarycontainer thereabout, insulation means between said primary andsecondary containers, and a plurality of frame means exterior of saidprimary container and lying in the respective planes of said first wallmeans, each of said first wall means including projecting edge portionsextending through the planes defined by the adjacent intersecting wallmeans, said projections being secured to .said frame means.

2. A container in accordance with claim 1 wherein said secondarycontainer is coextensive with the interior of said frame means.

3. A container in accordance with claim 1 wherein said projecting edgeportions of said first wall means are generally rectangular in form andspaced from their adjacent projections a distance equal to the width ofsaid projection.

4. A container in accordance with claim 3 including weld means forming abead at the intersection of said wall means along the boundaries of saidprojections to thereby form a sealed primary container.

5. A container in accordance with claim '3 including weld means formingan inner bead at the intersection of said wall means along the innermostboundaries of said projections to thereby form a sealed primarycontainer.

6. A flat walled polygonal container for storage of liquids at cryogenictemperature comprising a plurality of intersecting wall means defining acontainer, insulation means secured to the exterior surface of saidcontainer and a plurality of supporting frame means exterior of saidcontainer and lying in the respective planes of said wall means, each ofsaid wall means including projecting edge portions extending through theplane defined by the adjacent intersecting wall means, said projectionsbeing weldedly secured to said frame means.

'7. A fiat walled polygonal container for storage of liquids atcryogenic temperature comprising a plurality of first Wall meansdefining an inner primary container, a plurality of second wall meanssurrounding and spaced from said inner primary container defining anouter secondary container thereabout, and a plurality of frame meansexterior of said primary container and lying in the respective planes ofsaid first Wall means, each of said first wall means includingprojecting edge portions extending through the planes defined by theadjacent intersecting wall means, said projections being secured to saidframe means.

8. A container in accordance with claim 7 including insulation meansbetween said primary and secondary containers, said insulating meanssubstantially filling the space between said wall means to therebytransmit the hydrostatic load of the liquid within the container fromthe first wall means to the second wall means.

9. A container in accordance with claim 7 wherein said projecting edgeportions of said first wall means are generally rectangular'in form andequally spaced from their adjacent projections a distance equal to thewidth of said projection.

References Cited UNITED STATES PATENTS 2,306,275 12/1942 Murray 220152,892,564 6/1959 Morrison 220-15 3,039,418 6/1962 Versluis. 3,104,0259/1963 Dosker 22015 THERON E. CONDON, Primary Examiner.

JAMES R. GARRETT, Assistant Examiner.

1. A FLAT WALLED POLYGONAL CONTAINER FOR STORAGE OF LIQUIDS AT CRYOGENICTEMPERATURE COMPRISING A PLURALITY OF FIRST WALL MEANS DEFINING AN INNERPRIMARY CONTAINER, A PLURALITY OF SECOND WALL MEANS SURROUNDING ANDSPACED FROM SAID INNER PRIMARY CONTAINER DEFINING AN OUTER SECONDARYCONTAINER THEREABOUT, INSULATION MEANS BETWEEN SAID PRIMARY ANDSECONDARY CONTAINERS, AND A PLURALITY OF FRAME MEANS EXTERIOR OF SAIDPRIMARY CONTAINER AND LYING IN THE RESPECTIVE PLANES OF SAID FIRST WALLMEANS, EACH OF SAID FIRST WALL MEANS INCLUDING PROJECTING EDGE PORTIONSEXTENDING THROUGH THE PLANES DEFINED BY THE ADJACENT INTERSECTING WALLMEANS, SAID PROJECTIONS BEING SECURED TO SAID FRAME MEANS.